Eric...
I couldn't agree more !
I have become a strong believer in using a high quality (Delo, Rotella, ...)single wt dino oil.
My reasoning is exactly in line w/ your comments re: single vs multi Vis...
and
The points made in the article about additive packages used in the newer API rating multi Vis oils (especially Syn) that are pointed at Diesel emissions reg's and pollution control systems on autos & trucks... that don't apply to us and can actually cause problems.

I used to believe that the newer ratings were always backward integrated and superior - the article changed my opinions and it's the only one I've found that deals w/ marine applications.

Previous thread -Yanmar - Mobil 1 Synthetic My post #30 has several attached oil report files as well as a link to another thread w/100+ posts & MANY opinions.

The problem I've found with almost all oil reports & recommendation is that they are auto / over the road truck related - some gas engine some diesel but few marine related.

The attached file - Best lubricants for yacht engines - is the best / most applicable for our interests as diesel boat owners... I've changed my opinion and preference re: oils after reading this one - I have little interest in trying to convince anyone to change their opinion but rather to offer up what I felt was a good and relevant study... draw your own conclusions.

Thanks for the file and direction to # 30.

And thanks to ALL for engaging in this convoluted topic .. All your shared experiences are much appreciated .... F.B.

I definitely would't do what the previous owner did ... unless you do your research and find that he was indeed using an oil that is 100% suitable for the engine. The previous owner may not have known enough to choose the right oil. Another exception is when the PO was using what the engine manual recommends. Most all the time you can't go wrong w the engine manual.

However it is often said that one should stick w a brand over time and not mix the oils. Personally I mix viscosities but not oil brands. And some oil types should'nt be mixed.

I wouldn't recomend anything but straight 30W dino oil for a non-turbo engine. I don't know much about turbochargers so I'd need to do some research to make that call. Depending on the turbo cooling and how it's related to the lube oil you may find the turbo dosn't heat the lube oil at all. Then the oil type and viscosity could be the same as a NA engine. If the turbo make very high temps and is cooled by the lube oil I would use a synthetic lube. If it's warmer than a NA engine but only slightly a synthetic blend and multi-viscosity 15W-40 would probably be good. Check the manual.

Shell Rotella and RPM Delo are of equal quality. Shell seems to be an east coast brand and Delo is very dominant especially in Alaska. Both excellent. For synthetic I don't know what's best. I have a bias against one brand but it has to do w ultralight aircraft 2 stroke application.

I definitely would't do what the previous owner did ... unless you do your research and find that he was indeed using an oil that is 100% suitable for the engine. The previous owner may not have known enough to choose the right oil. Another exception is when the PO was using what the engine manual recommends. Most all the time you can't go wrong w the engine manual.

I would be cautious in changing with one regard. if you switch to an oil w/ high detergent after long use of non detergent type oil. from what i've read in the forum it could be a problem. Don't know firsthand thou.

for my engines i just buy oil from cummins (in the blue cans) ...it isn't synthetic & it's obviously what they "recommend" for their engines.
trying to save money on oil is not my goal, but in fact the "cummins" oil is cheaper than major branded oil i can buy !
one trip for oil & filters...too easy ?